In the prior art, the method of conventional valve actuation for a vehicle engine is well known and its application has more than one hundred years of history. However, due to the additional requirements on engine emission and engine braking, more and more engines need to produce an auxiliary engine valve event, such as an exhaust gas recirculation event or an engine braking event, in addition to the normal engine valve event. The engine brake has gradually become the must-have device for the heavy-duty commercial vehicle engines.
The engine braking technology is also well known. The engine is temporarily converted to a compressor, and in the conversion process the fuel is cut off, the exhaust valve is opened near the end of the compression stroke of the engine piston, thereby allowing the compressed gases (being air during braking) to be released. The energy absorbed by the compressed gas during the compression stroke cannot be returned to the engine piston at the subsequent expansion stroke, but is dissipated by the engine exhaust and cooling systems, which results in an effective engine braking and the slow-down of the vehicle.
There are different types of engine brakes. Typically, an engine braking operation is achieved by adding an auxiliary valve event for engine braking event into the normal engine valve event. Depending on how the auxiliary valve event is generated, an engine brake can be defined as:                1. Type I engine brake: the auxiliary valve event is introduced from a neighboring existing cam in the engine, which generates the so called Jake Brake;        2. Type II engine brake: the auxiliary valve event generates a lost motion type engine brake by altering existing cam profile;        3. Type III engine brake: the auxiliary valve event is produced from a dedicated cam for engine braking, which generates a dedicated brake valve event via a dedicated brake rocker arm;        4. Type IV engine brake: the auxiliary valve event is produced by modifying the existing valve lift of the engine, which normally generates a bleeder type engine brake; and        5. Type V engine brake: the auxiliary valve event is produced by using a dedicated valve train to generate a dedicated valve (the fifth valve) engine brake.        
An example of engine brake devices in the prior art is disclosed by Cummins in U.S. Pat. No. 3,220,392. The engine brake system based on the patent has enjoyed a great commercial success. However, this engine brake system is a bolt-on accessory that fits above the engine. In order to mount the brake system, a spacer needs to be positioned between the cylinder and the valve cover. This arrangement may additionally increase height, weight, and cost to the engine.
Among these above five types of engine brakes, the third one, i.e. the dedicated cam or the dedicated rocker arm brake, has the best engine brake power. However, the existing dedicated rocker arm brake device cannot be applied to the engines with the valve bridge being parallel or almost parallel to the rocker arm.